Service Function Chaining Guanglei Li
Guanwen Li
Taixin Li
Qi Xu
Huachun Zhou
Internet Draft Beijing Jiaotong University
Intended status: Informational October 10, 2017
Expires: April 2018
Hybrid Hierarchical Multi-Domain Service Function chainingdraft-li-sfc-hhsfc-03.txt
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Internet-Draft Hybrid Hierarchical Multi-domain SFC October 2017
The document [I-D.ietf-sfc-control-plane] describes requirements for
conveying information between SFC control plane and data plane in a
SFC-enabled domain. The document [I-D.dolson-sfc-hierarchical]
proposes a hierarchical SFC for multiple domains, which are
controlled by a single organization and trusted by each other, and
focus on data plane. [I-D. unify-sfc-control-plane-exp] provides an
insight into a Service Function Chain (SFC) control and Network
Function Virtualization (NFV) orchestration proof of concept
implementation and experimentation in multi-domain/technology
environments, which adopts a recursive control plane, but does not
consider the business model between different virtual network
providers or infrastructure providers to support a SFC spanning
domains with different ownership.
In this document, we consider SFCs traversing different domains
owned by different organizations (e.g., ISPs) or by a single
organization with administration partitions, which means an
overarching orchestrator or manager is infeasible for multi-domain
SFC.
The Hybrid Hierarchical SFC combines flat distributed control plane
and centralized hierarchical control plane. A centralized recursive,
hierarchical control plane is recommended to be deployed into a
large domain consisting of smaller sub-domains while a flat
distributed control plane is recommended to be deployed into
multiple large domains.
1.1. Scope
The "domain" discussed in this document is a logical concept. Domain
division depends on circumstances including but not limited to: geo-
location, technology, administration, or ownership.
This document focus on control plan. [I-D.dolson-sfc-hierarchical]
gives many discussions about data plane, especially internal
boundary node (IBN) path configuration, where methods to manipulate
NSH are still practicable in this document.
In a recursive hierarchical control plane, an upper level plane is
responsible to abstract lower level plane's topologies and
services. A mapping element is also needed in every control plane
level. The control protocol, abstraction, mapping mechanism and
interfaces are out of this document's scope.
In a flat distributed control plane, horizontal interfaces are used
to realize state sharing, context translation and policies
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Internet-Draft Hybrid Hierarchical Multi-domain SFC October 2017
negotiation between domains. The protocol is out of this document's
scope.
1.2. Terminology
o Sub-domains: Smaller domains in a large administration/physical
domain.
o Multi-Domain Service Function Chaining A service function
chaining pass through multiple domains.
o SFC eXchange Platform: A logical entity that is used for the
negotiation between domains. It can be a trusted third-party
platform (e.g., deployed in future software defined IXP) or built
by a single owner between heterogeneous networks.
o Abstraction Element (AE) A logical entity that abstracts the
lower-level topology and services.
o Mapping Element (ME) A logical entity that map upper-level
instructions to lower-level control entities.
o Path Calculation Element (PCE): A logical entity that computes
service function paths (SFP).
o Information Base Element (IBE): A logical information base entity
that stores topology and service information acquired from the
abstraction element and provide them to the mapping element and
path calculation element.
1.3. Assumptions
We assume flexible and dynamic SFCs are based on Software Defined
Networking (SDN) and NFV. Distributed NFV crossing different domains
makes the hybrid hierarchical control plane necessary.
Network virtualization and network function virtualization create
new business models such as service function as a service, e.g., a
third-part Software Defined IXP (SDX) between ISPs can provides a
negotiation platform to support Multi-domain SFC.
In this document, a domain consists of sub-domains and every sub-
domain has its own control plane. A single-level control plane is
impractical considering the scalability and complexity of control
plane.
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Internet-Draft Hybrid Hierarchical Multi-domain SFC October 2017
subdomain optimization in a centralized way. For a lower-level
control plane, it only cares about the governed sub-domain.
Mapping Elements are responsible to translate the upper-level
instructions, which could contain abstracted services requirements,
service quality and overlay forwarding behaviors, to the lower-level
control instances.
Each level control plane has its own Information Base Elements.
Abstraction elements create, update or delete the information in
Information Base Elements. The information is utilized by Mapping
Elements and Path Calculation Elements.
2.2.2. Inter-domain
Horizontal interfaces should be deployed in the top-level control
plane to realize inter-domain communication, including State sharing,
context translation and policies negotiation.
Considering the circumstance that domains owned by different ISPs
connected by the Internet eXchange Ports, which could be a datacenter
implemented SDN technology in the future, a SFC eXchange Platform
(SXP) was proposed to support rich business models between different
organizations. Their distributed, multi-domain nature makes it
possible to enable a highly customized multi-domains SFC.
Figure 2 shows a SFC eXchange Platform connecting three different
domains. Figure 3 shows an overview of layered domains and SFC
eXchange Platform. In a function as service business model, inter-
domain path computation can be driven by service agreements.
Horizontal interfaces should be designed between domains and SFC
eXchange Platform. Figure 4 shows domains connected by distributed
SFC eXchange Platform. SFC eXchange Platforms server as brokers,
which orchestrate multi-domains SFC in a distributed way.
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Internet-Draft Hybrid Hierarchical Multi-domain SFC October 2017
+-------+ +-------+ +-------+
| | +--------+ | | +--------+ | |
| | | SFC | | | | SFC | | |
|Domains<--->eXchange<--->Domains<--->eXchange<--->Domains|
| | |Platform| | | |Platform| | |
+-------+ +--------+ +-------+ +--------+ +-------+
Figure 4: Distributed SFC eX Platforms
2.3. Data plane2.3.1. Intra-domain
The discussion about SFC data plane components in top levels and
lower levels in the document [draft-ietf-sfc-hierarchical-02] can be
applied in the recursive hierarchical domain defined by this
document.
2.3.2. Inter-domain
When packets go out of a domain, the inter-domain NSH should be
added. Using unique path is recommended to manipulate inter-domain
NSH.
When domains are connected by SDN-enabled SFC eXchange Platforms,
which act as SFFs for Multi-domain SFC, the SFC eXchange Platforms
will forwarding traffics according to the inter-domain SPI/SI.
3. SFC eXchange Platform
The inter-domain traffic classify rules should be negotiated and
decided by administrators of each domain with service agreements and
policies. Distributed SFC eXchange Platforms select the service
function location from multiple candidate domains.
3.1. Inter-domain negotiation
As a trusted third-party platform, the SFC eXchange platform may not
orchestrate the Multi-Domain SFC directly. In other words, it only
exchanges and collect domains' service states and policies. Every
domain can decide their own multi-domain SFP according to the states
and agreements. The SFC eXchange Platform implements the negotiation
results and decisions for domains, such as flow-specific peering.
Based on the SFC eXchange Platform, rich business models may appear.
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